Modern x-ray diffraction experiments use x-ray tubes that are optimized to deliver a line focus or a point focus onto the sample. The optimal type of focus depends on the details of the experiment being performed. For example, for experiments involving standard powder samples, a line focus is the preferred geometry while, for two dimensional diffraction or single crystal diffraction measurements, a point focus is preferred. However, as many users may have the need to conduct experiments on different types of samples, it may be desirable to switch between point and line focus as the situation warrants. Conventionally, this is accomplished by exchanging the optics mounted on the x-ray tube. For example, a single mirror used to redirect the x-ray beam produces a line focus, and this mirror can be exchanged with a pair of focusing mirrors (e.g., a so-called “Kirkpatrick-Baez” mirror pair), which will create a point focus.
Although functional, the changing of x-ray optics presents several drawbacks. Firstly, the optics must be exchanged manually, (and must typically be realigned after the exchange), which is inconvenient, labor-intensive and time consuming. Secondly, when a point focus optic is installed on the line focus port of an x-ray tube, it tends to focus only the x-rays from a small fraction of the tube onto the sample. As such, the x-ray flux achieved is smaller than that which could be achieved by using a point focus port. The point focus port is a port that is located at 90 degrees relative to the line focus port, and is oriented at a shallow, oblique angle relative to the electron beam focus, and which thereby projects the electron line focus on the anode into an apparent x-ray spot.
In U.S. Pat. No. 5,515,414 an x-ray tube is provided with flexible cooling water connections that allow the position of the x-ray tube to changed by 90 degrees to switch between point focus and line focus modes. However, to make the change, the tube must be removed from the tube shield, rotated manually, and reinserted into the shield. The optics used with either configuration appears to be the same, unlike the prior art systems described above.
U.S. Pat. No. 4,866,749 describes an x-ray tube with two cathodes: one that, when energized, produces a point focus; and the other that produces a line focus. When in the different modes, the optics used appear to remain the same. In addition, only the electron focus on the anode is changed and not the inclination of the anode, so that the point focus has a relatively low intensity.